Image display device

ABSTRACT

Provided is an image display device including an optical scanner configured to scan light emitted from a light source, a parallel light generator configured to generate the scanned light as parallel light, a prism configured to refract the parallel light, and a light direction changer including a plurality of points whereon the parallel light refracted by the prism is incident and configured to reflect or diffract the parallel light and change a traveling direction of the parallel light, wherein the prism is provided on a path of each light traveling from the optical scanner to the light direction changer to adjust an optical path difference of parallel light incident on each of the plurality of points of the light direction changer.

CROSS-REFERENCE TO RELATED APPLICATION

This application in a continuation of U.S. application Ser. No.16/148,026, filed Oct. 1, 2018, which claims priority from JapanesePatent Application No. 2017-194273, filed on Oct. 4, 2017, in theJapanese Patent Office, and Korean Patent Application No.10-2018-0088669, filed on Jul. 30, 2018, in the Korean IntellectualProperty Office, the disclosures of which are herein incorporated byreference in their entireties.

BACKGROUND 1. Field

Example embodiments relate to image display devices.

2. Description of the Related Art

Recently, technologies for displaying images with high resolution onimage display devices have been actively developed. For example, ahead-up display is an image display device that displays a clearer imageby correcting chromatic aberration of light emitted from a light sourcethrough a prism.

The head-up display may include optical information display means suchas a cathode ray tube (CRT), an optical system projecting light emittedfrom the optical information display means in a predetermined direction,and a screen that the light reaches. The optical system may include aplurality of lenses and mirrors to adjust the traveling direction oflight emitted from the CRT to reach the screen.

SUMMARY

One or more example embodiments provide image display devices having adisplay surface with uniform resolution.

According to an aspect of an example embodiment, there is provided animage display device including an optical scanner configured to scanlight emitted from a light source, a parallel light generator configuredto generate the scanned light as parallel light, a prism configured torefract the parallel light, and a light direction changer including aplurality of points whereon the parallel light refracted by the prism isincident, and configured to reflect or diffract the parallel light andchange a traveling direction of the parallel light, wherein the prism isprovided on a path of each light traveling from the optical scanner tothe light direction changer, and is configured to adjust an optical pathdifference of parallel light incident on each of the plurality of pointsof the light direction changer.

The prism may include a wedge prism.

The optical path difference may be adjusted by changing an apex angle ofthe wedge prism.

The prism may have an apex angle such that the optical path differenceis 0.

The prism may include glass or resin.

The optical scanner may include a micro electro mechanical systems(MEMS) mirror.

The parallel light generator may include a parabolic mirror.

The parallel light generator may include a condenser lens.

The image display device may further include a plane mirror providedbetween the prism and the light direction changer and configured toreflect light refracted from the prism to be incident on the lightdirection changer.

The image display device may further include a screen on which lighthaving a traveling direction changed by the light direction changer isincident, and an optical system provided between the screen and thelight direction changer and configured to guide the light to be incidenton the screen.

The image display device may further include a diffuser between thelight direction changer and the optical system, wherein the diffuser isconfigured to diffuse the light incident from the light directionchanger.

A surface of the light direction changer may include a reflective typepattern element.

A surface of the light direction changer may include a reflective typeelement having a cross-sectional pattern of a plurality of rectangularprism shapes.

A surface of the light direction changer may include a reflective typeelement having a cross-sectional pattern of a plurality of triangularprism shapes.

A surface of the light direction changer may include a reflective typeelement having a cross-sectional pattern of a plurality ofsemi-cylindrical shapes.

A surface of the light direction changer may include a reflective typeelement having a cross-sectional pattern of a plurality of parabolicshapes.

A surface of the light direction changer may include a reflective typepattern element having a pattern of a plurality of spherical concavelens array.

A surface of the light direction changer may include a reflective typepattern element having a pattern of a plurality of parabolic concavelens array.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects will become apparent and more readilyappreciated from the following description of the example embodiments,taken in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view showing an image display device accordingto an example embodiment;

FIG. 2 is a side sectional view showing a side surface of the imagedisplay device of FIG. 1 according to an example embodiment;

FIG. 3 is a cross-sectional view showing a configuration example of animage display device according to a related example;

FIG. 4 is a diagram for explaining a change in a beam diameter of alaser beam propagated by the image display device of FIG. 3 according toan example embodiment;

FIG. 5 is a table showing an example of a relationship between anincidence angle of a laser beam with respect to a pattern element, amaximum optical path difference of the laser beam, and a difference inbeam diameters of the image display device of FIG. 3 according to anexample embodiment;

FIG. 6 is a table showing an example of a relationship between anincidence angle of a laser beam with respect to a light directionchanger of FIGS. 1 and 2, a maximum optical path difference of the laserbeam, and an apex angle according to an example embodiment;

FIG. 7 is a perspective view showing an image display device accordingto an example embodiment;

FIG. 8 is a cross-sectional view showing the image display device ofFIG. 7 according to an example embodiment;

FIG. 9 is a cross-sectional view showing an image display deviceaccording to an example embodiment;

FIG. 10 is a cross-sectional view showing an image display deviceaccording to an example embodiment;

FIG. 11 shows a modification of a light direction changer included inimage display devices according to example embodiments;

FIG. 12 shows a modification of a light direction changer included inimage display devices according to example embodiments;

FIG. 13 shows a modification of a light direction changer included inimage display devices according to example embodiments;

FIG. 14 shows a modification of a light direction changer included inimage display devices according to example embodiments;

FIG. 15 shows a modification of a light direction changer included inimage display devices according to example embodiments;

FIG. 16 shows a modification of a light direction changer included inimage display devices according to example embodiments; and

FIG. 17 shows a modification of a light direction changer included inimage display devices according to example embodiments.

DETAILED DESCRIPTION

Reference will now be made in detail to example embodiments, examples ofwhich are illustrated in the accompanying drawings, wherein likereference numerals refer to like elements throughout. In this regard,the example embodiments may have different forms and should not beconstrued as being limited to the descriptions set forth herein.Accordingly, the example embodiments are merely described below, byreferring to the figures, to explain aspects.

Throughout the specification, it will be understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof. Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list. Forexample, the expression, “at least one of a, b, and c,” should beunderstood as including only a, only b, only c, both a and b, both a andc, both b and c, or all of a, b, and c.

FIG. 1 is a perspective view showing an image display device 100according to an example embodiment.

FIG. 2 is a side sectional view showing a side surface of the imagedisplay device 100 of FIG. 1 according to an example embodiment.

The image display device 100 may include, for example, a head-updisplay, a head-mounted display, a projector, or the like, but is notlimited thereto and may include other image display devices.

Referring to FIGS. 1 and 2, the image display device 100 may include anoptical scanner 120 (for example, a micro electro mechanical system(MEMS) mirror) scanning light emitted from a light source, a parallellight generator 130 generating the scanned light as parallel light, aprism 110 refracting the parallel light, a plane mirror 140 reflectingthe refracted parallel light that passed through the prism 110, and alight direction changer 150 (e.g., a pattern element) changing thetraveling direction of the light reflected by the plane mirror 140.

The light emitted from the optical scanner 120 may be the parallel lighttraveling through a plurality of paths by the parallel light generator130. The parallel light may be incident on the plane mirror 140 afterpassing through the prism 110. The parallel light incident on the planemirror 140 may be reflected and become incident on the light directionchanger 150. The direction of the light incident on the light directionchanger 150 may be changed and projected on a screen. An optical pathdifference that may cause a non-uniform resolution of the screen mayoccur between the lights incident on the light direction changer 150through the plurality of paths. The prism 110 may adjust the opticalpath difference between the lights. That is, the prism 110 may reduce oreliminate the optical path difference between the lights. The operatingprinciple of the prism 110 for adjusting the optical path differencewill be described later with reference to FIG. 6.

The optical scanner 120 may include a MEMS mirror. The MEMS mirrorfunctions as the optical scanner 120 scanning a laser beam (for example,red light, green light, blue light, or a combination thereof) emittedfrom a light source by driving of two axes in the horizontal andvertical directions. The MEMS mirror may project an image onto the lightdirection changer 150. The optical scanner 120 may include the MEMSmirror, but is not limited thereto, and may include a member capable ofemitting a laser beam other than the MEMS mirror. The optical scanner120 may also include a member capable of emitting light other than thelaser beam. Further, the light emitted from the optical scanner 120 maybe incident on the parallel light generator 130.

The parallel light generator 130 may cause the light emitted from theoptical scanner 120 to travel in rays parallel to each other. Theparallel light generator 130 may include a parabolic mirror. When thelight emitted from a focal position of the parallel light generator 130is reflected at each point of the parallel light generator 130, thetraveling direction of each reflected light may be parallel to theoptical axis of the parallel light generator 130. Therefore, byarranging the optical scanner 120 at the focal position of the parallellight generator 130, the light emitted from the optical scanner 120 maybe reflected by the parallel light generator 130 and be parallel lighttraveling in a parallel direction. Also, a member other than theparabolic mirror may be used as long as the member may make the lightemitted from the optical scanner 120 parallel to the optical axis. Forexample, FIGS. 7 and 8 show an image display device 200 that uses acondenser lens 131 instead of the parabolic mirror. Further, forexample, a collimator lens may be used instead of the parabolic mirror.However, example embodiments are not limited thereto. The parallel lightreflected from the parallel light generator 130 may be incident on theprism 110.

The prism 110 may be refract the light reflected by the parallel lightgenerator 130. The prism 110 may be, for example, a wedge prism havingan apex angle α. The prism 110 may be provided on a path of each lighttraveling from the optical scanner 120 to the light direction changer150 and may adjust the optical path difference of each light from theoptical scanner 120 to the light direction changer 150 throughrefraction to be 0 or less than a predetermined value. Therefore, theimage display devices 100 and 200 may adjust a difference in a beamdiameter of the light direction changer 150 to be 0 or less than apredetermined value.

In FIGS. 1 and 2, the prism 110 is illustrated as a triangular prismhaving a triangular shape in which the apex angle α is not a rightangle, but is not limited thereto. More specifically, as long as theoptical path difference of each laser beam is adjusted to be 0 or lessthan the predetermined value, a rectangular prism in which the apexangle α is a right angle may be used, or a prism having any polyhedralshape may be used. Further, the laser beam transmitted through the prism110 may be incident on the plane mirror 140. The apex angle α of theprism 110 capable of adjusting the optical path difference to be 0 orless than the predetermined value will be described later.

The plane mirror 140 may be provided between the prism 110 and the lightdirection changer 150 and may reflect the light that passed through theprism 110 and allow the light to be incident on the light directionchanger 150. The plane mirror 140 may reflect the parallel laser beamtransmitted through the prism 110 and allow the parallel laser beam tobe incident on the light direction changer 150 while maintaining aparallel state.

The light direction changer 150 may include a pattern element. The lightdirection changer 150 may include a plurality of points where theparallel light refracted by the prism 110 and reflected by the planemirror 140 is incident thereon. The pattern element may include apredetermined pattern on a surface. Examples of the pattern will bedescribed later with reference to FIGS. 11 to 17. The travelingdirection of the laser beam reflected by the plane mirror 140 may bechanged by reflection or diffraction by the pattern of the patternelement. For example, by adjusting intervals of slits and an aspectratio of the pattern element, the traveling direction of the lightreflected from the plane mirror 140 may be changed to the frontdirection with respect to the pattern element.

The material of the pattern element is not particularly limited. Forexample, a wire grid may be used to form the predeterminedconcave-convex pattern on a surface of the pattern element.

FIG. 3 is a cross-sectional view showing a configuration example of animage display device 1000 according to a related example.

FIG. 4 is a diagram for explaining a change in a beam diameter of alaser beam propagated by the image display device 1000 of FIG. 3.

Referring to FIG. 3, the image display device 1000 may include a MEMSmirror 10, a parabolic mirror 20, and a pattern element 30. In therelated example, a prism included in an example embodiment is notprovided. Light, for example, a laser beam emitted from the MEMS mirror10 may be incident on the pattern element 30 as parallel light that isparallel to an optical axis 21 by the parabolic mirror 20. The patternelement 30 may change the traveling direction of the incident parallellight and project the parallel light onto a screen.

An optical path difference of a laser beam may occur in the imagedisplay device 1000, which may cause a difference in resolution of thescreen. More specifically, an optical path of a laser beam reflected ata point A of the parabolic mirror 20 and incident on a surface end pointa of the pattern element 30 may be greater by an optical path differenceΔOP than an optical path of a laser beam reflected at a point B of theparabolic mirror 20 and incident on a surface end point b of the patternelement 30. For example, when a length V of the pattern element 30 fromthe end point a to the end point b is 83.2 mm and an incidence angle θis 50.0 degree, the optical path difference ΔOP may be about 63.735 mmby Equation 1 below.

ΔOP=cos(90−θ)·V  (Equation 1)

FIG. 4 shows a beam diameter along the traveling direction of the laserbeam. Referring to FIG. 4, light having a strong directivity such as thelaser beam and that propagates straight ahead may have the beam diametergradually narrowing to a certain position and then gradually widening.Here, the beam diameter of the position where the beam diameter is thenarrowest is referred to as a beam waist Wo. Resolution may be thehighest at the beam waist Wo. Further, beam diameters before and afterthe beam waist Wo may have a similarity relationship.

Referring to FIG. 3, to maximize the resolution of a display imagegenerated on a surface of the pattern element 30, a position of eachoptical element may be necessarily adjusted such that the beam waist Wois positioned on the surface of the pattern element 30. When the beamwaist Wo is adjusted to be located at a center point c (the center pointbetween the end points a and b) of the surface of the pattern element 30(that is, the beam diameter at the center point c is Wo) the resolutionof the display image of the center point c may be the highest. Forexample, in case where an optical path difference between the lightincident on the end point a or b and the light incident on the centerpoint c is ΔOP/2, a beam diameter W of the end point a and the end pointb may be greater than the beam waist Wo. In this case, the resolution ofa display image of the end point a and the end point b may be lower thanthe resolution of the display image of the center point c.

Meanwhile, the beam waist Wo in the case of assuming an ideal Gaussianbeam may be calculated by Equation 2 below. The beam diameter W of theend point a and the end point b may be calculated by Equation 3 below.In Equation 2, A denotes a wavelength of the laser beam.

$\begin{matrix}{{Wo} = {2 \cdot \left( {\left( \frac{\Delta\; O\; P}{2} \right) \cdot \frac{\lambda}{\pi}} \right)^{\frac{1}{2}}}} & \left( {{Equation}\mspace{14mu} 2} \right) \\{W = {{Wo} \cdot 2^{\frac{1}{2}}}} & \left( {{Equation}\mspace{14mu} 3} \right)\end{matrix}$

FIG. 5 is a table showing a specific example of the relationship betweenthe incidence angle θ of a laser beam with respect to the patternelement 30, the maximum optical path difference ΔOP of the laser beam,and a difference in beam diameters of the image display device 1000 ofFIG. 3.

The optical path difference ΔOP shown in FIG. 5 may be obtained by usingEquation 1, and the length V from the end point a to the end point b ofthe pattern element 30 may be 83.2 mm.

Referring to FIG. 5, the relationship of the incidence angle θ, theoptical path difference ΔOP, the beam waist Wo may be calculated byusing Equation 2, and the beam diameter W may be calculated by usingEquation 3. For example, the laser beam may be incident on the patternelement 30 such that the incident angle θ is 7.7 degrees. In this case,the maximum optical path difference ΔOP may be 11.171 mm, the beam waistWo may be 0.061 mm, and the beam diameter W may be 0.086 mm at a pointaway from the beam waist Wo by ΔOP/2. The larger the incident angle θ,the greater the difference in the beam diameter on the surface of thepattern element 30, and thus lower the resolution of a display image.Also, the beam waist Wo and the beam diameter W of FIG. 5 may becalculated when the wavelength A of Equation 2 is about 523 nm.

As described with reference to FIGS. 3, 4, and 5, the image displaydevice 1000 may have a non-uniform resolution according to an opticalpath difference occurring between laser beams incident on the patternelement 30 and a characteristic of the beam diameter W varying dependingon traveling position of the laser beam. Meanwhile, the image displaydevice 100 according to an example embodiment of FIGS. 1 and 2 may havea uniform resolution by including the prism 110 adjusting the opticalpath difference between laser beams and reducing or eliminating theoptical path difference.

FIG. 6 is a table showing a specific example of a relationship betweenthe incidence angle θ of a laser beam with respect to the lightdirection changer 150 of FIGS. 1 and 2, a maximum optical pathdifference ΔOP of the laser beam, and the apex angle α.

As described above, the prism 110 may adjust an optical path differenceof each light from the optical scanner 120 to the light directionchanger 150. The prism 110 may adjust the optical path difference to be0 or less than a predetermined value. Therefore, the image displaydevice 100 may adjust a difference in a beam diameter of the lightdirection changer 150 to 0 or less than the predetermined value.

For example, the image display device 100 may change the beam diameter Win the light direction changer 150 to be the same as the beam waist Wo.An optical path length L of the prism 110 (the traveling path of lightin the vacuum) may be calculated from Equation 4 below by a path lengthD (the actual length through which light travels) of the prism 110 and arefractive index n of the prism 110.

L=n·D  (Equation 4)

In other words, when the prism 110 has the refractive index n largerthan 1, the optical path length L may be greater than the path length D.This principle may be used to adjust the optical path difference of thelight traveling in a plurality of paths. The installation position andthe installation angle of each member and the apex angle α of the prism110 may be determined such that the optical path difference is 0 or lessthan the predetermined value.

For example, when the length V from one end of the light directionchanger 150 to the other end is 83.2 mm and the incidence angle θ of thelaser beam with respect to the light direction changer 150 is 50.0degree, the maximum optical path difference ΔOP may be 63.735 mmaccording to Equation 1. The apex angle α of the prism 110 that makesthe maximum optical path difference ΔOP almost zero may be determined as57.15 degree. Also, FIG. 6 is only an example, and each value may varydepending on the installation position and the installation angle ofeach member.

When the refractive index n is greater than 1, a material of the prism110 is not particularly limited. For example, the material of the prism110 may include glass, resin, or the like. Since the Abbe number ofglass tends to be greater than that of resin, the difference in therefractive index n caused by the wavelength difference of the laser beammay be reduced by using glass as the material of the prism 110. Also, itmay be easier to process glass than resin in a plane manner.

FIG. 7 is a perspective view showing an image display device 200according to an example embodiment.

FIG. 8 is a cross-sectional view showing the image display device 200 ofFIG. 7.

Referring to FIGS. 7 and 8, the image display device 200 is the same asthe image display device 100 shown in FIGS. 1 and 2, except that theparallel light generator 130 of FIGS. 1 and 2 is replaced by a condenserlens 131.

FIG. 9 is a cross-sectional view showing an image display device 300according to an example embodiment.

Referring to FIG. 9, the image display device 300 may include atranslucent screen 160 at the front end of the light direction changer150 and an optical system 161 between the light direction changer 150and a screen 160. The optical system 161 may allow a laser beam to beincident on the screen 160. Accordingly, the image display device 300may function as a head-up display. The screen 160 may display a virtualimage by using the laser beam incident through the optical system 161. Auser may recognize the virtual image.

FIG. 10 is a cross-sectional view showing an image display device 400according to an example embodiment.

Referring to FIG. 10, the image display device 400 may further include adiffuser 162 between the light direction changer 150 and the opticalsystem 161. Accordingly, a laser beam incident from the light directionchanger 150 may be focused on the diffuser 162. The diffuser 162 mayserve as a secondary image plane. The diffuser 162 may diffuse theincident laser beam, thereby expanding a visual region which is a regionwhere a display image may be recognized. Also, the configurations ofFIGS. 9 and 10 are merely examples, and the arrangement of the screen160, the optical system 161, and the diffuser 162 may be changed.

Also, the configurations discussed above are merely examples, and theconfigurations of the image display devices 100, 200, 300, and 400 arenot limited thereto. For example, the image display devices 100, 200,300, and 400 may not include the plane mirror 140. More specifically,when each laser beam is incident on a surface of the light directionchanger 150 at the predetermined incident angle θ or the optical pathdifference of each laser beam is close to 0, the plane mirror 140 may beomitted.

Also, the above-described example embodiments may be applied to anyimage display device other than a head-up display. For example, theimage display devices 100, 200, 300, and 400 may include a projectionoptical system at the front end of the light direction changer 150 toserve as a projector. As described above, the image display devices 100,200, 300, and 400 may include an arbitrary optical system at the frontend of the light direction changer 150 to operate as different types ofimage display devices.

FIG. 11 shows a top view and a cross-sectional view of a modification ofthe light direction changer 150 included in the image display devices100, 200, 300, and 400 according to example embodiments.

Referring to FIG. 11, the light direction changer 150 may include areflective type pattern element. The light direction changer 150 mayhave a wire grid or the like on its surface to form a pattern. Forexample, the light direction changer 150 may have a shape in which aplurality of rectangular shape prisms are disposed in parallel such thatthe prisms face a front direction with respect to the light directionchanger 151. Intervals of slits and an aspect ratio of the pattern maybe determined such that the traveling direction of a first orderdiffracted ray is a front direction with respect to the light directionchanger 150. Also, the traveling direction of a laser beam changed bythe light direction changer 150 is not limited to the front directionwith respect to the light direction changer 150 and may be changedaccording to the configurations of the image display devices 100, 200,300, and 400.

FIG. 12 shows a top view and a cross-sectional view of a modification ofa light direction changer 151 included in the image display devices 100,200, 300, and 400 according to example embodiments.

Referring to FIG. 12, the light direction changer 151 may include areflective type pattern element having a pattern of a rectangular prismshape on its surface. For example, the light direction changer 151 mayhave a shape in which a plurality of sawtooth shape prisms are disposedin parallel such that the prisms face a front direction with respect tothe light direction changer 151. The light direction changer 151 maychange the traveling direction of a laser beam to a predetermined firstdirection by reflecting the laser beam on an inclined surface formed onthe surface.

FIG. 13 shows a top view and a cross-sectional view of a modification ofa light direction changer 152 included in the image display devices 100,200, 300, and 400 according to example embodiments.

Referring to FIG. 13, the light direction changer 152 may include areflective type pattern element having a pattern of a prism shape on itssurface. More specifically, the light direction changer 152 may have ashape in which a plurality of triangular prisms are disposed in parallelsuch that the apex angle α is directed forward with respect to the lightdirection changer 152. The light direction changer 152 may change thetraveling direction of a laser beam to a predetermined first directionby reflecting the laser beam on an inclined surface formed on thesurface.

FIG. 14 shows a top view and a cross-sectional view of a modification ofa light direction changer 153 included in the image display devices 100,200, 300, and 400 according to example embodiments.

Referring to FIG. 14, the light direction changer 153 may include areflective type pattern element having a pattern of a plurality ofcylindrical shapes disposed in parallel on its surface. The cylindricalshape includes a semi-cylindrical shape in which a part of a cylinder iscut off. The light direction changer 153 may change the travelingdirection of a laser beam by reflecting the laser beam on the surface ofthe cylindrical shape. Also, since the light direction changer 153 hasthe semi-cylindrical shape on the surface, the laser beam may bereflected and then travel, be diffused, in various directions accordingto a position where the laser beam is reflected from. Therefore, thelight direction changer 153 may expand a visual region.

FIG. 15 shows a top view and a cross-sectional view of a modification ofa light direction changer 154 included in the image display devices 100,200, 300, and 400 according to example embodiments.

Referring to FIG. 15, the light direction changer 154 may include areflective type pattern element having a pattern of a plurality ofparabolic shapes disposed in parallel on its surface. More specifically,the light direction changer 154 may have any parabolic shape on thesurface. The light direction changer 154 may change the travelingdirection of a laser beam by reflecting the laser beam on the parabolicsurface. Also, since the light direction changer 154 has the parabolicshape on its surface, the laser beam may be reflected and then travel,be diffused, in various directions according to a position where thelaser beam is reflected from. Therefore, the light direction changer 154may expand a visual region, like the light direction changer 153 of FIG.14.

FIG. 16 is a top view and a cross-sectional view showing a modificationof a light direction changer 155 included in the image display devices100, 200, 300, and 400 according to example embodiments.

Referring to FIG. 16, the light direction changer 155 may include areflective type lattice element having a pattern of a spherical concavelens array shape on its surface. The light direction changer 155 maychange the traveling direction of a laser beam by reflecting the laserbeam on the surface. Further, since the light direction changer 155 hasa surface shape where spherical concave lenses are arranged in a latticearray shape, the laser beam may be reflected and then travel, bediffused, in various directions according to a position where the laserbeam is reflected. Therefore, the light direction changer 155 may expanda visual region, like the light direction changer 153 of FIG. 14.

FIG. 17 is a top view and a cross-sectional view showing a modificationof a light direction changer 155 included in the image display devices100, 200, 300, and 400 according to example embodiments.

Referring to FIG. 17, the light direction changer 156 may include areflective type lattice element having a pattern of a parabolic concavelens array shape on its surface. The light direction changer 156 maychange the traveling direction of a laser beam by reflecting the laserbeam on the surface. Further, since the light direction changer 156 hasa surface shape like that parabolic concave lenses are arranged in alattice array shape, the laser beam may be reflected and then travel, bediffused, in various directions according to a position where the laserbeam is reflected. Therefore, the light direction changer 156 may expanda visual region, like the light direction changer 153 of FIG. 14.

Also, the surface of the parabolic concave shape may have acharacteristic of reflecting parallel light and converging light at afocus position. That is, since the laser beam reflected from the surfaceof the parabolic concave shape converges at a focus position of eachparabolic surface, a second focal plane may be generated by theconvergence of focus positions of parabolic surfaces. Thereby, the imagedisplay device 100 may allow a user to recognize as if a display imageis being projected on a plurality of focal planes. In other words, theimage display device 100 may realize the 3D display by controlling thedisplay content time-serially according to a direction in which thelaser beam is reflected by the light direction changer 156.

Also, a material and a manufacturing method of each member used as thelight direction changers 150 to 156 described with reference to FIGS. 11to 17 are not particularly limited.

As described above, each of the image display devices 100, 200, 300, and400 according to example embodiments may include the optical scanner 120scanning light emitted from a light source, the parallel light generator130 generating the scanned light as parallel light, the prism 110refracting the parallel light, and the light direction changer 150changing the traveling direction of the light. The prism 110 may adjustthe optical path difference of each light to be substantially 0 or lessthan a predetermined value. Therefore, the image display devices 100,200, 300, and 400 may adjust the difference in the beam diameter on thelight direction changer 150 to be substantially 0 or less than thepredetermined value. For example, the image display device 100 maychange the beam diameter on the light direction changer 150 to be thesame as a diameter of the beam waist Wo.

According to example embodiments of the present disclosure, uniformityof resolution of a display by an image display device may be improved.

It should be understood that embodiments described herein should beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments.

While one or more example embodiments have been described with referenceto the figures, it will be understood by those of ordinary skill in theart that various changes in form and details may be made therein withoutdeparting from the spirit and scope as defined by the following claims.

What is claimed is:
 1. An image display device comprising: an opticalscanner configured to scan light emitted from a light source; a parallellight generator configured to generate the scanned light as parallellight; a prism configured to refract the parallel light and output theparallel light refracted; and a light direction changer comprising aplurality of points whereon the parallel light refracted and output bythe prism is incident, and configured to reflect or diffract theparallel light and change a traveling direction of the parallel light,wherein the prism is provided on a path of each light traveling from theoptical scanner to the light direction changer, and is configured toadjust an optical path difference of parallel light incident on each ofthe plurality of points of the light direction changer, and wherein theprism comprises a first surface on which the parallel light is incidentand a second surface through which the parallel light refracted isoutput external to the prism.
 2. The image display device of claim 1,wherein the prism comprises a wedge prism.
 3. The image display deviceof claim 1, wherein the prism comprises glass or resin.
 4. The imagedisplay device of claim 1, wherein the optical scanner comprises a microelectro mechanical systems (MEMS) mirror.
 5. The image display device ofclaim 1, wherein the parallel light generator comprises a parabolicmirror.
 6. The image display device of claim 1, wherein the parallellight generator comprises a condenser lens.
 7. The image display deviceof claim 1, further comprising: a plane mirror provided between theprism and the light direction changer, and configured to reflect lightrefracted from the prism to be incident on the light direction changer.8. The image display device of claim 1, further comprising: a screen onwhich light having a traveling direction changed by the light directionchanger is incident; and an optical system provided between the screenand the light direction changer and configured to guide the light to beincident on the screen.
 9. The image display device of claim 8, furthercomprising: a diffuser between the light direction changer and theoptical system, wherein the diffuser is configured to diffuse the lightincident from the light direction changer.